This invention relates to a process for the polymerization of ethylene or .alpha.-olefins for providing polymers with an improved particle size distribution and a high stereoregularity, and a catalyst therefor.
The most typical Ziegler catalysts which are used for the polymerization of ethylene or .alpha.-olefins comprises a titanium compound-containing catalyst component and an organoaluminum compound.
It is well-known that a catalyst activity is improved by pulverizing a titanium catalyst component such as titanium trichloride and its compositions (for example, Japanese Patent Publications No. 14125/60 and No. 24271/64), by copulverizing the titanium component with various compounds (for example, Japanese Patent Publications No. 24270/64, No. 24272/64, No. 10065/68, British Pat. No. 1087314, U.S. Pat. No. 3,764,591, Japanese Application Kokai Nos. 48-68497, 48-29694, 48-38295 and 49-53196), or by subjecting these pulverized products to a modification treatment with an organic solvent or its mixtures with a modifier agent (for example, U.S. Pat. No. 3,850,899, Japanese Patent Publication Nos. 48638/74, 17319/75, 48637/74 and British Pat. No. 1370559).
However, when such pulverization and modification treatments are conducted, the resulting titanium catalyst component is, in general, remarkably broadened in the particle size distribution and thus, more than 10% by weight of the particles has a size smaller than 5 microns.
When homopolymerization or copolymerization of ethylene or .alpha.-olefins is carried out using a catalyst comprising a titanium catalyst component and an organoaluminum compound, the particle size of the resulting polymer or copolymer is markedly influenced by the particle size of the titanium component used. Thus, using the titanium component having a wide particle size distribution, in which fine particles are included in large quantities, the resulting homopolymers or copolymers have a wide particle size distribution, in which fine powders of less than 50 microns are usually included in an amount of 10 to 30% by weight.
When the polymers obtained have a wide particle size distribution and particularly, contain a large amount of fine powders, separating of the polymers from a solvent by filtrating or centrifuging encounters a difficulty and further, owing to scattering of the polymer fine powders in the drying and pelletizing steps, the loss of polymers increases. Thus, superfluous equipments must be provided for overcoming such disadvantages so that the production of polymer must be conducted by the complicated process. Therefore the improvement has been required.
Various methods for improving a catalyst activity have been proposed as mentioned above. Among them a modification treatment of the starting titanium trichloride by various modifiers is disclosed, for example, in U.S. Pat. No. 3,850,899, Japanese Patent Publication No. 48638/74 and British Pat. No. 1370559. As set forth in Comparative Examples given hereinafter, these methods are effective to some degree with respect of improvements in the catalyst activity, however, during the modification treatment the titanium trichloride component is divided to fine particles so that the preparation of polymer in a commercial scale encounters difficulties as mentioned above.